1. Field of the Invention
The present invention relates to a socket with a detection function, and more particularly to a network socket that detects a type of an inserted plug according to voltage variation of a detection pin.
2. Description of the Prior Art
Currently, fool-proof designs of an RJ-45 network socket are still not good enough, so a phone cable plug of a type similar to a network cable plug, e.g. an RJ-11 plug, can be easily inserted into the network socket. However, since a great difference exists between signals carried on phone cables and network cables, when the phone cable plug is wrongly inserted into the network socket, not only may back-end electronic devices of the network socket be damaged, but the phone-line circuit loop may also enter a short-circuit state, causing the phone line to appear to be engaged.
For example, please refer to FIG. 1. FIG. 1 is a schematic diagram of a circuit loop between a telephone set 11 and a branch exchange 12 in a conventional public switched telephone network (PSTN). When the telephone set 11 is not picked up, or on the hook, a hook switch 112 is in an open-circuit state. At this time, a DC operating voltage that the branch exchange 12 supplies to the telephone set 11, i.e. a voltage between Tip 13 and Ring 14, roughly lies between 36 and 60 volts depending on the country. When alerting an incoming call, an AC ring signal of about a hundred volts (40 to 150 Vpp) is superimposed over the DC operating voltage to ring the telephone set 11 by the branch exchange 12. Therefore, when the phone cable plug is wrongly inserted into the network socket, the back-end electronic devices of the network socket, such as a notebook computer, may be damaged due to inability to bear such high voltages as the DC operating voltage and the AC ring signal. In addition, please refer to FIG. 2. FIG. 2 is a schematic diagram of a pulse transformer 20 built in a conventional network socket. The pulse transformer 20 includes input terminals RX0+ to RX3+, RX0− to RX3− and output terminals TX0+ to TX3+, TX0− to TX3−, for receiving and outputting network signals, respectively, and is utilized for enhancing reception reliability of the network socket by filtering electromagnetic interference from the high frequency differential signals. As shown in FIG. 2, when the phone cable plug is wrongly inserted into the network socket, the Tip 23 and the Ring 24 are respectively coupled to the input terminals RX2+ and RX2−, and since the input terminals RX2+ and RX2− are short-circuited inside the pulse transformer 20, the phone-line circuit loop is then operated in a state similar to an off-hook state of the hook switch 112 in FIG. 1, causing the phone line to seem to be engaged.
On the other hand, since the trend of the notebook computer is toward lightweight and small size development, less space is available at the periphery of the notebook computer for installing input/output ports, except for batteries, optical drives, and cooling fans, so if the phone cable sockets and the network cable sockets could be integrated, the space occupied by these sockets will be reduced effectively.